Method of and device for measuring the wear in a gun barrel



June 27, 1957 CARL'GUSTAV SJULIN 3,327,518

METHOD OF AND DEVICE FOR MEASURING THE WEAR IN A GUN BARREL Filed Feb. 15, 1965 1 N VEN TOR. CARL ausmv .SJdL/N BY MW United I States Patent 3,327,518 METHOD OF AND DEVICE FOR MEASURING THE WEAR IN A GUN BARREL Carl-Gustav Sjiilin, Bofors, Sweden, assignor to Alrtiebolaget Bofors, Bofors, Sweden, a corporation of Sweden Filed Feb. 15, 1965, Ser. No. 432,617 Claims priority, application Sweden, Apr. 6, 1964,

4,213/ 64, Patent 202,560 5 Claims. (Cl. 73-7) ABSTRACT OF THE DISCLOSURE The invention relates to a method of and a device for measuring the wear in a gun barrel by providing as test or reference unit a hollow plug made of the same material as the barrel, weighing the plug, firing the plug through the gun barrel and again weighing the plug. The difference in weight then constitutes a measure of the wear experienced by the gun barrel.

The invention relates to a method of measuring the wear in a gun barrel or other tubular launching device due to the firing of a projectile by gases propelling the projectile through the barrel. The invention also relates to a device for measuring the wear in a gun barrel or other tubular launching device as a result of the firing of projectiles.

The wear which is experienced by the gun barrel is primarily due to mechanical and thermal action. The thermal wear is caused by the heat of the propellant gases, and extensive investigation has shown that the mechanical wear is most probably a function of the thermal wear.

It is of great importance for a manufacturer'of gun barrels and other tubular launching devices for firing projectiles and also for a manufacturer of propellants to ascertain in' an economical manner and with sufficient accuracy how many projectiles can be fired through a gun barrel before the wear in such barrel exceeds the acceptable tolerances. I 7

One of the conventional Wear tests heretofore used is to fire projectiles through the gun barrel until the barrel is worn beyond acceptable limits. The barrels used for such tests are selected at random from a production run and the projectiles used for the tests are also selected at random from a production run.

As it is evident, wear tests of this kind are expensive and time consuming. The number of projectiles which are required to'carry out the tests is very considerable and projectiles are expensive. The gun barrels used for the tests are also expensive and the labor costs tend to be considerable.

It has also been proposed to make a wear test by forming a plug having a hole therethrough out of the material to be used for making the barrels in a production run. Such plug is inserted into a so-called Vieilles erosion bomb. A quantity of the propellant to be used for firing projectiles through the barrels or other devices to be tested is placed in the bomb and ignited. As a result of the flow of the generated propellant gases through the hole in the plug, the plug experiences a certain erosion and the resultant decrease in the weight of the plug then constitute a measure of the Wear experienced by the plug. The wear of the plug thus ascertained permits conclusions as to the wear which may be expected for gun barrels made from the material used for the plug when projectiles are fired through the barrels by means of the propellant used for the test.

However, it has been found that the characteristics of the combustion of the propellant in such a test bomb are ice entirely different from the characteristics of the combustion as actually occurring in a gun barrel. In a bomb, the maximum pressure is obtained almost immediately upon the complete ignition of the propellant and the gases pass through the hole in the plug without performing any useful Work. As a result, the combustion gases reach rapidly the maximum flame temperature which is most probably maintained during a considerable part of the discharge period. Hence, the difference in erosion as measured for different propellants and for different materials used for forming the test plugs, such as suitable steel alloys, depend primarily upon the flame tempera ture of the gases and the discharge time rather than upon the combustion characteristics of the propellant as occurring in the barrel. Consequently, the measured relations between the erosion effects caused by different propellants, for instance, different types of powder, used in a test bomb, are primarily a function of the explosion heat of the powder. There are very little, if any at all, affected by the physical structure of the grains of powder and the variations in the combustion characteristics as caused by the differences in the physical structure of the grains of powder. Extensive tests and analysis have shown that the measured values as obtained by firing an erosion bomb of the conventional type as hereinbefore described are highly deceptive and are of very little practical value for determining the wear which a barrel will experience when projectiles are actually fired through the same.

It is a broad object of the invention to provide a novel and improved method of accurately, simply and inexpensively measuring the wear actually experienced by a gun barrel or other tubular launching device due to the action of the propellant gases when a projectile is fired through the barrel or other device.

A more specific object of the invention is to provide a novel and improved method of measuring the wear in a gun barrel upon firing a projectile therethrough, which method utilizes the principle of a test plug as hereinbefore referred to in a novel and improved manner in that the thermal action experienced by the plug when a flow of propellant gases is directed therethrough substantially duplicates the thermal action experienced by the gun barrel when a projectile is fired through the same. Accordingly, the wear experienced by the plug provides an accurate measure for the wear in a gun barrel when a projectile is actually fired through the same.

Another more specific object of the invention is to provide a novel and improved testing method of the general kind above referred to which yields fully satisfactory measuring data from comparatively few test firings. Ten test firings are generally suflicient. In some instances, a somewhat greater number of test firings may be advisa-' ble, such as tento twenty test firings, but in any case, very much less than were heretofore necessary when tests were carried out by firing projectiles through a barrel.

It is also an object of the invention to provide a novel and improved plug for carrying out the method of the invention.

Basically, the method and the plug according to the invention may be used for gun barrels of all calibers, but it is particularly suitable for calibers above 20 millimeters.

The aforementioned objects, features and advantages of the invention and other objects, features and advantages which will be pointed out hereinafter are attained by providing a plug having a hole therethrough and made of the same material as the barrel, the wear of which is to be measured and also a projectile having a lengthwise hole therethrough. The plug is weighed and then secured in the projectile in a position in which the hole in the plug and the hole in the projectile are in lengthwise alignment thereby providing a continuing channel extending through the length of the projectile. The projectile with the plug inserted therein is thereupon fired through the gun barrel by the action of propellant gases. The plug is then removed from the projectile and again weighed. The difference in the weight of the plug before and after firing as caused by the flow of gases through the channel in the plug and the projectile is accurately indicative of the Wear in barrels to be tested when projectiles are fired through the same by means of the propellant gases used for the test firings.

In the single figure of the accompanying drawing, a preferred embodiment of the invention is shown by way of illustration and not by way of limitation.

The figure shows an elongated preferably solid projectile 1 through which extends an axial bore 2. This hole is partly widened at to accommodate a plug 4 Which is made of the same material as the gun barrel which it is intended to test with respect to erosion due to thermal and mechanical wear. A lengthwise hole 3 through the plug is in alignment with the hole 2 through the projectile to form a continuous channel extending through the length of the body of the projectile. The outer wall of the plug is preferably tapered toward the nose of the projectile and the widened wall portion 5 of hole 2 is correspondingly shaped. The plug is inserted into the projectile from the rear end thereof and secured in position by suitable retaining means such as an externally threaded ring 6 which is screwed into a recess 7 formed in the rear end face of the projectile. A driving band 8, preferably made of copper, is provided in a conventional manner.

Instead of single continuing holes 2 and 3 through the projectile, several parallel continuing holes may also be provided.

An erosion test according to the invention is carried out as follows:

First, the weight of the plug is ascertained. The plug is then inserted into the widened hole portion 5 and secured in the projectile by means of screw ring 6. The projectile with a plug inserted therein is then inserted into the chamber of the gun barrel to be tested and a supply of suitable propellant material is placed behind the plug. The propellant material may be placed in a cartridge case to which the projectile is secured. In other words, the described test projectile and plug may be assembled in substantially the same manner as any round of ammunition.

The projectile is fired through the barrel by igniting the propellant in a conventional manner and the flow of propellant gases will cause the same wear in the barrel as it is caused by firing a conventional projectile through the same. As is evident, the action of the propellant gases upon the inner wall of the hole 3 in the plug when flowing through the same will have exactly the same wear characteristics as they have upon the inner wall of the barrel. In other Words, the inner wall surface of the, test plug will be subjected to exactly the same gas flow as the inner wall surface of the barrel.

After firing the projectile, the same is recovered, the plug is removed and again weighed. The difference in weight before and after firing then constitutes a true measure of the thermal wear experienced by the barrel. If it be desired, a test projectile with a test plug inserted therein may be fired several times before the plug is removed and weighed.

The method of the invention and the device for carrying out the method also constitute simple and economical means of testing and comparing different types of propellant materials without the necessity of carrying out the aforedescribed very expensive and time consuming conventional testing operations.

While the invention has been described in detail with respect to a certain now preferred example and embodiment of the invention, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. A method of measuring the Wear in a barrel due to the firing of a projectile by the action of propellant gases, said method comprising the steps of providing a plug having a hole therethrough and being made of the same Ina-- terial as the barrel the wear of which is to be measured and a projectile having a lengthwise hole therethrough; weighing the plug; securing the plug in the projectile in a position in which the holes in the plug and the projectile are in lengthwise alignment thereby providing a continuing channel through the projectile; firing the projectile with the plug inserted therein through the barrel by the action of propellant gases; and weighing. the plug again after firing whereby the difference in the weight of the plug before and after firing is indicative of the wear experienced by the barrel due to the action of the propellant gases.

2. A device for measuring the wear in a barrel due to the firing of a projectile by the action of propellant gases,- said device comprising a projectile having a hole therethrough, and a test plug having a hole therethrough and made of the same material as the barrel the wear of which is to be tested, said plug being detachably secured in said projectile in a position in which the hole in the projectile and the hole in the plug are in alignment to provide a continuing lengthwise channel through the projectile and the plug.

3. A device for measuring the wear in a barrel due to the firing of a projectile by the action of propellant gases, said device comprising an elongated projectile having a lengthwise hole therethrough, and an elongated plug having an axial hole therethrough and made of the same material as the barrel the wear of which is to be tested, said plug being detachably secured in said projectile in a position in which the holes through the projectile and the plug are in lengthwise alignment to form a continuous lengthwise channel through the projectile and the plug.

4. A device for measuring the wear in a barrel due to the firing of a projectile by the action of propellant gases, said device comprising a plug having a hole therethrough and made of the same material as the barrel the wear of which is to be measured, an elongated projectile having in its rear end wall a recess and an axial hole extending from said recess throughout the length of the projectile, said plug being inserted into said hole of the projectile in a position in which the holes in the plug and the projectile are in axial alignment, and retaining means fitted in said recess for detachably retaining said plug in the recess.

5. A device according to claim 4 wherein said plug is tapered towards the nose of the projectile, said hole in the projectile including a widened tapered portion to accommodate said tapered plug with a close fit.

References Cited UNITED STATES PATENTS 2,478,659 8/1949 Jackson, et al 73-7 DAVID SCHONBERG, Prim'ary Examiner. 

1. A METHOD OF MEASURING THE WEAR IN A BARREL DUE TO THE FIRING OF A PROJECTILE BY THE ACTION OF PROPELLANT GASES, SAID METHOD COMPRISING THE STEPS OF PROVIDING A PLUG HAVING A HOLE THERETHROUGH AND BEING MADE OF THE SAME MATERIAL AS THE BARREL THE WEAR OF WHICH IS TO BE MEASURED AND A PROJECTILE HAVING A LENGTHWISE HOLE THERETHROUGH; WEIGHING THE PLUG; SECURING THE PLUG IN THE PROJECTILE IN A POSITION IN WHICH THE HOLES IN THE PLUG AND THE PROJECTILE ARE IN LENGTHWISE ALIGNMENT THEREBY PROVIDING A CONTINUING CHANNEL THROUGH THE PROJECTILE; FIRING THE PROJECTILE WITH THE PLUG INSERTED THEREIN THROUGH THE BARREL BY THE ACTION OF PROPELLANT GASES; AND WEIGHING THE PLUG AGAIN AFTER FIRING WHEREBY THE DIFFERENCE IN THE WEIGHT OF THE PLUG BEFORE AND AFTER FIRING IS INDICATIVE OF THE WEAR EXPERIENCED BY THE BARREL DUE TO THE ACTION OF THE PROPELLANT GASES. 